The gate is also called feeding port, which is the channel connecting the diverging channel and the cavity melt. The selection of the gate is directly related to whether the injection molding products can be injected in good condition and high quality. Gate design includes gate section shape and size determination and gate location selection. In the design of injection mold, according to the structure and characteristics of gate, there are 11 kinds of sprue.
1. Sprue gate: it is the main runner gate, which belongs to the non-restrictive gate.
(1) advantages: the plastic melt is directly entered into the cavity by the large end of the main channel, so it has the characteristics of small flow resistance, short process and long supply time. Such a gate has a good melt flow state, the melt from the center of the core of the cavity flow to the parting surface, which is beneficial to the exhaust; This kind of gate form makes injection molding and pouring system have the minimum projection area on the parting surface, the mold structure is compact, and the injection molding machine is uniform.
(2) disadvantages: feed has a larger residual stress, easy to cause the injection parts buckling deformation, the gate is larger at the same time, remove the gate mark is difficult and trace is bigger, affect beautiful, so this type of gate more long used in large and medium-sized injection molding process, deep cavity, cylindrical or shell injection molding products, particularly suitable for polycarbonate and polysulfone plastic viscosity. In addition, this type of gate is only suitable for single cavity mold.
In the design of this type of gate, in order to minimize contact with plastic injection products in the gate area, prevent it from shrinkage, deformation defects such as mouth, on the one hand, should try to choose a smaller taper of the mainstream way cone Angle (for 2 ~ 4 °), on the other hand should be reduced as far as possible to determine template and the thickness of the mold base.
2. Side gate: the side gate is called the standard gate. Side gate opening in the parting surface, plastic melt from the medial or lateral fills the mold cavity, the cross section shape is rectangular (flat slot) more, change the gate width and thickness can adjust the shear rate of melt and gate freeze time. This kind of gate can choose its position according to the shape feature of the injection molded products, and it is convenient to process and repair, so it is widely used.
(1) advantages: small section of gate section can reduce the consumption of pouring system melt, easy to remove and not obvious trace. It is suitable for all kinds of injection molding products, but it is not suitable for long and thin barrel shaped plastic products.
(2) disadvantages: the injection molding products and sprue can not be separated by themselves, there is a fusion mark, and the injection pressure loss is large, which is unfavorable to the exhaust of the injection molded products in the deep cavity.
3. Fan gate: fan gate, generally open on the parting surface, from the external side of the cavity, the gate is gradually widened along the feeding direction, and the thickness is gradually reduced. The plastic melt from the gate into the cavity is relatively flat, which can reduce the warping deformation and is suitable for the plate shaped plastic products with larger width.
4. Sheet gate: also known as flat seam gate. The distribution channel of gate is parallel to the side of the cavity, and its length is usually greater than the width of plastic products.
Advantages: (1) the plastic melt through the thin gate at a relatively low rate evenly into the cavity, the flow and material flow in parallel can avoid warping deformation, commonly used to shape flat large thin-wall plastic products.
(2) disadvantages: it is difficult to remove the gate, thus increasing the production cost of plastic products.
5. Ear protection gate: the earthen gate is mainly used for high and transparent plastic products and plastic products with small deformation requirements.
Advantages: (1) TAB gate is in open ears slot on the side of the cavity, the melt through the gate on the ear canal side friction heat, so as to improve the liquidity, after adjust the direction and speed, in the earmuffs evenly and smoothly into the cavity, can avoid the jets.
(2) disadvantages: it is more difficult to remove the gate, and the gate marks are larger.
6. Point gate: the point gate is especially suitable for cylindrical, shell and box-shaped plastic products. For larger flat plastic products, multiple point gate can be set to reduce warping deformation. For the thin-walled plastic products, the shear rate near the gate is too high, the residual stress is large and easy to crack, and the wall thickness of the gate is increased locally.
(1) advantages: small gate position, small gate mark, and the gate can be automatically cut when opening mold, which is conducive to automatic operation.
(2) disadvantages: the injection pressure is large, and in most cases, it must adopt the three-plate mold structure, the mold is relatively complicated and the molding cycle is long.
(1) advantages: the latent gate position is relatively flexible, and can be used in the plastic products inside and outside the surface. The flow path is opened on the parting surface, the gate infiltrates into the parting surface, the melting material is inclined to enter the cavity. Due to the setting of the extruding mechanism in the plastic products and the runner, the gate is automatically cut off when the mold opening is opened, and the flow path is automatically detached. At the same time, the mould structure is simple, which greatly improves the production efficiency and reduces the cost.
(2) disadvantages: it is not applicable to the plastic that is too tough or too brittle, the former is not easy to cut off, the latter is easy to break, and the gate is easily blocked.
Gate 8. The moon shape: shape of the moon gate is actually a form of circular arc form latent type of the gate structure, generally used in junior, by directly into the parting surface glue way, made of two pieces of insert split, the distributary channel and gate design on the insert.
(1) advantages: it can be injected into the bottom of the product, which has the characteristics of a point gate. The gate marks are small and can be automatically pulled off when the top is out, which is easy to realize automation. If the head of the pin is turned into a cone, it can be set up in the channel to push out.
(2) disadvantages: the shape is more complex and needs to be processed with electrode.
9. Ring gate
It is called ring gate to fill the cavity with circular feed.
(1) advantage: the feed is uniform, the flow velocity is roughly the same on the circumference, and the flow state is good. It is easy to eliminate the air in the cavity and avoid the welding mark. Because the gate is designed on the core, the ring gate is mainly used for forming cylindrical plastic products.
(2) disadvantages: the pouring system consumes more material, the gate is removed, and the gate marks are obvious.
10. Umbrella gate: the umbrella gate is a special form of ring gate, which is mainly used for the high quality and high quality tubular plastic products.
(1) advantage: the feed is even, no weld mark is produced, and the exhaust is good.
(2) disadvantages: the removal of the runner must be machined, which increases the cost.
11. Disc gate: disc gate is actually the apex Angle of 180 ° umbrella gate, used for inner hole larger cylindrical plastic products, or have large rectangular inner hole of the plastic products, surrounding the gate in the inner hole.
(1) advantages: with the characteristics of an umbrella gate, the plastic melt is injected into the cavity in a roughly synchronous manner around the inner hole, and the core force is uniform, which can avoid the welding mark and exhaust smoothly.
(2) disadvantages: it will leave obvious gate marks on the inner edge of plastic products.