Analysis of common problems in PVC profile mold debugging

1、Mold plugging

At the exit of the die,if the average speed of each part of the parison is equal,and the influence of self weight is not considered,the parison uniformly extruded will also be affected by three aspects:

(1)Melt off mold expansion;

(2)Parison draft contraction;

(3)Parison cooling shrinkage.

When the drawing speed of the parison at the exit of the die is less than the extrusion speed of the parison under the action of the tractor,the phenomenon of die plugging will occur.

The main reasons for mold plugging are as follows:

1.The tractor slips and the traction force is too small.(remove the water on the surface of the profile and adjust the positive pressure of the upper and lower tracks)2 The speed of the tractor is unstable,fast and slow.(check the tractor)3 The material is too plastic,and the parison cannot support the traction force(reduce the barrel temperature)4 The temperature is out of control,and the discharge on one side is too fast.(check thermocouple)5 The vacuum degree of the setting mold or water tank is too large,and the resistance of the profile is large.(adjust vacuum)6 The lubricant in the formula is excessive,the fluidity is too strong,and the extrusion speed is unstable.(adjust lubricant proportion)7 The feeding slope at the jaw opening of the feeding end of the setting die is too small and too short.(lengthen the feeding slope*)8 The discharge at the jaw mouth is too fast(blowing air for cooling or stopping the machine to repair the discharge*)9 The gap at the jaw opening of the setting die is larger in front and smaller in rear(check whether the positioning system of the setting die and the template are installed incorrectly)

2、Vibration

If the resistance of the profile in the traction process is too large,vibration will occur(Sanjia is called"shaking").If the profile is vibrated during production,it must form vibration lines perpendicular to the traction direction on the surface of the profile,which will seriously affect the apparent quality of the profile,and the wear of the mold is relatively fast,affecting the service life of the mold.There are two main reasons for resistance.One is that the vacuum is too strong during production.On the other hand,the mold size is unreasonable.When repairing the mold,first ensure to repair the mold size under the premise of reasonable vacuum.Reasonable vacuum refers to the minimum vacuum degree under the condition of ensuring the overall size of the profile and the flatness of the large surface.In order to remove the resistance,priority should be given to repairing the shaped block,and attention should be paid to ensuring the size of the shape control point.Point a at four points in Figure 1 is the control point of the overall dimension of the product.If the overall dimension of the profile has been at zero or negative difference,point a cannot be repaired by removing materials at this time.For the size of point B,attention should be paid to the fitting size of the batten after assembly.If point B gives way too much,under the action of negative pressure,the upper claw of the batten groove protrudes,causing the batten to turn outward,and the fitting size is large.

If the resistance cannot be completely removed by repairing the sizing block,then consider repairing the sizing die.Since the whole profile cannot pass through the sizing die,you can use a saw blade to saw a part of the profile to feel the resistance through the sizing die.Vibration is sometimes caused by improper repair of other problems,especially after fusion welding at the jaw,pay attention to give way to the corresponding parts.

Try not to use unconventional means such as dropping oil at the inlet of the setting mold or adding soap to the water tank to eliminate the vibration,otherwise the cooling water will be polluted,and the small water hole is easy to be blocked by scale.

3、Pant

During the production process,the medium-sized billets cannot stably enter the setting mold,sometimes in contact with the setting mold,sometimes separated,just like people's breathing is very short after intense exercise,this phenomenon is called panting.The most intuitive expression of wheezing is that the vacuum gauge of stereotyped model 1 has been swinging all the time.The gasping phenomenon is relatively difficult to repair compared with other common problems of profiles.The causes of wheezing can be considered from the following aspects:

1.Resistance.When panting,the resistance of shaping will not be too large,too large will vibrate,because the resistance is not obvious,it is not easy to find.At this time,the resistance can be found through the method of local molding.For example,the hanging wall of the flat open frame is completely molded first,and the time is counted.According to the traction speed,the number of shaped blocks will be calculated,and then there will be problems.Then try each jaw separately in turn.

2.Vacuum.When gasping,the vacuum must be unstable.At this time,it is necessary to seal the places where there may be air leakage between each section of the setting mold and between the setting mold and the water tank.After sealing,if the vacuum is too large,it may cause great resistance.Open several vacuum ports on the machine tool to deflate.

3.The parison is too plastic,and the traction force cannot be well transmitted during parison shaping.At this time,the barrel temperature should be appropriately reduced.

4.The discharge at the jaw is too slow,and the filling is not enough to set the mold,resulting in air leakage.

4、Profile size out of tolerance

1.Overall dimension

If the overall dimension is out of tolerance,first consider whether the size of the shape control point is correct.When the shape is positive or negative,you can directly give way to the rear shaping block.When the shape is negative,and the difference from the nominal size is large,you need to increase the size of the shape control point of the shaping die.When the difference is small,you can directly repair the size of the shape control point of the shaping block in front of the water tank.At this time,you must pay attention to the displacement of the corresponding parts.Otherwise,shaking and panting may occur.

If the size of the shape control point is correct,the size of the jaw must be small.At this time,the feeding can be increased to make the jaw full so that the overall dimension can meet the tolerance requirements.

If the overall upper and lower dimensions of the profile are too small,pay attention to whether it is caused by the excessive pressure of the tractor.

2.Wall thickness

When repairing the wall thickness,it is strictly forbidden to repair the die size

3.Functional bayonet size

If the size of the rubber strip opening or pressing strip opening is too large,first pay attention to whether the shape control point a is correct.If the shape is positive or negative,repair point A.if the shape is at zero or negative,repair point B.

If the size of the rubber strip opening or pressing strip opening is too small,first pay attention to whether the shape control point a is correct.If the shape is negative,repair point A.if the shape is at zero or positive,repair point B.

If it is necessary to repair the size of the shape control point a,repair it from the rear setting block when removing the material,and try to repair welding from the beginning of the setting mold when adding the material.

If the size is too small,repair welding at point a needs to be done on the outside.

The above repair plan is on the premise that the discharge of the claw mouth is consistent with or slightly slower than the large surface.

4.Fit size

After the main profile is matched with the batten,the matching size a is often too large.At this time,it is necessary to decide whether to repair the batten or the main material according to the actual production situation.If you repair the batten,you can reduce the size of B on the batten to make the batten"buckle"so as to solve the problem.Reducing the size of B on the batten can repair point C or point D.when repairing point C,you can"pick the angle"between the machine head and the sizing.Affected by the parting,point C on the sizing die is not easy to repair,while point D can be processed directly by the milling machine,which is relatively convenient.If the main material is repaired,it is necessary to increase the size of B on the main material.Increasing the size of B can be repaired by welding on the shaped block at point E or milling 0.1mm-0.2mm at point F(when the overall size of the small surface goes negative or zero,the method of milling point F is preferred to repair and cooperate)

5、Profile shape out of tolerance

1.Profile bending

The root cause of profile bending is that there is residual stress in the profile during the production process,and there are two main reasons for the formation of residual stress,one is that the cooling is not synchronized,and the other is that the resistance of each part of the profile during traction is inconsistent.Bending caused by asynchronous cooling mainly includes the following situations:

A.The die head is unevenly discharged,and the wall thickness varies greatly.At this time,if the cooling efficiency of each part is consistent,the profile is easy to bend to the side with thicker wall thickness;

B.The die head heating system is out of control,resulting in uneven discharge;

C.The cooling system of the setting mold is unreasonable,and the cooling efficiency of each part is inconsistent.If the profile is bent to the N side,the water hole on the W side can be blocked or the vacuum on the N side can be increased.(the water hole on the shaping block on the stuffy W side is very effective)

D.The traction speed is too fast,because the cooling efficiency of all parts of the sizing cooling system cannot be the same.When the speed is slow,it can meet the cooling sizing requirements,and the difference of cooling efficiency does not play a leading role.However,when the extrusion speed is too fast,the side with poor cooling efficiency can no longer meet the requirements of cooling sizing,and the profile will bend to the side with poor cooling efficiency.Bending caused by resistance mainly includes the following situations:

A.The setting straightness is incorrect

B.The speed of the upper and lower tracks of the tractor is inconsistent

C.The resistance of each part of the profile is inconsistent,mainly in the large surface and the jaw resistance.Sometimes I feel helpless when repairing the bending problem of the profile.I use various methods,and the profile is indifferent.This is because bending is the result of cooling and resistance.For example,the push-pull box shown in the figure can be bent to the left and right.The known condition is that the cooling efficiency of the claw mouth side is better than that of the guide rail side(because there are many single walls at the claw mouth,which are double-sided cooling).If the profile is bent to the guide rail side,it is difficult to judge whether it is due to resistance or bending.Because increasing the vacuum makes the profile close to the fixed mold.Although the cooling efficiency increases,it also increases the resistance on the guide rail side.At this time,the water passage hole on the jaw side of the sizing block can be tightly sealed to reduce the cooling efficiency on the jaw side,and then the corner of the sizing block on the guide rail side can be made way to reduce the resistance.

If the profile bends to the jaw side,it means that the resistance on the jaw side is greater than that on the guide rail side.At this time,the water passage hole on the guide rail side of the sizing block can be tightly sealed to reduce the cooling efficiency on the guide rail side,and then reduce the sizing block resistance on the jaw side.

Try not to use the method of adjusting the straightness of the water tank to eliminate bending,because after adjustment,the resistance is large,the die wears fast,and the resistance is too large,which has a certain impact on the physical properties of the profile.Bending caused by any reason can be solved by adding baking device to eliminate internal stress.In addition,the setting mold can be separated from the water tank for a certain distance,and the profile can be cooled freely for a period of time to eliminate the internal stress.At this time,it should be noted that the distance should not be too long,otherwise the profile shape cannot be guaranteed.

2.Profile angle dimension

After the same profile is sawed into two sections,the gap a as shown in the figure appears after it is leveled on the horizontal plane,which is called the angular dimension out of tolerance of the profile.The out of tolerance of the profile angle dimension is caused by the distortion of the profile itself,which can be divided into left and right distortion and up and down distortion.

The left and right twist is very easy to repair,which can be solved by installing eccentric keys on the molding plate of the molding die or directly repairing welding on one side of the molding block and giving way to the other side.Twist up and down(typically,the suspension wall is upturned).At this time,it is very troublesome to repair the suspension wall directly.The shaped block on the lower side of the suspension wall should give way,and the upper side needs to be repaired and pressed.In fact,at this time,the mold repair method consistent with the left and right distortion can be used to solve it.