Diesel Engine Flywheel Papers


1. Field Problem Description and Cause Analysis

1.1 on-site process problems: In the pouring process, due to insufficient coating strength and unreasonable design of the pouring system, the runner was broken by high-temperature liquid metal, resulting in sand rolls, resulting in defects such as sand holes on the casting surface, resulting in scrapping.

1.2 reason analysis(1) When the group type is coated with paint, the sprue and the inner runner are coated too few times, and the paint is too thin, resulting in insufficient strength;(2) Excessive use of hot melt adhesive when the group type adheres to the runner causes excessive gas emission at the bonding part and increases the overall exhaust difficulty of the casting mold;(3) The model is not completely dried, and the model cluster has dead corners. The coating is not easy to dry when drying, which affects the strength. (4) The design of the gating system is unreasonable, the cross-sectional area of the adhesion part between the sprue is too large, and the spacing between the model cluster castings is too small, resulting in excessive air pressure in the model cluster. (5) Insufficient negative pressure and poor exhaust.

2. Solutions

2.1 Model Making and Group Type

(1) All model clusters shall be painted three times when painting paint. Each part of the paint shall be evenly painted to avoid too large a difference in paint thickness. The sprue adhesion part and dead corner part can be brushed more appropriately to fully ensure the dry strength of the paint. (2) The drying time shall be controlled at 6-8 hours after each coating, and the temperature of the drying room shall be controlled at 50±3 ℃, when burying the box, the self-inspection of the model cluster mainly depends on whether the dead corner part has been completely dried;(3) When bonding the model, follow the principle of hot melt adhesive (smear at the outer contour of the cross-sectional area), and strictly prevent the phenomenon of excessive use of hot melt adhesive;

2.2 gating system design

(1) A pouring system with vertical pouring-top pouring method is designed according to the concept of lost matrix pouring that can stand and do not lie down. The advantages of this pouring system are less consumables (shorter sprue design, shorter metal liquid filling process to reduce temperature loss during metal liquid flow), simple and convenient model making and grouping, coating hanging and embedding and box modeling, and easy removal of gate riser; the disadvantage is that the flywheel is disc-shaped, and vertical casting may affect its balance.

2) In order to overcome the problem of balance deviation caused by vertical casting, a pouring system with flat casting method is designed. This kind of pouring system has many consumables, difficult model making and group type, high cost and difficult removal of pouring riser, but it does not affect the balance of castings.

  

Fig. 1 vertical casting Fig. 1 horizontal casting

2.3 pouring parameters

1) Material: HT250

2) pouring temperature: 1350~1380 ℃

3) pouring time: 20~25s

4) Negative pressure:-0.04 ~ -0.06mp

5) shape density: 18~20g/L

6) Coating thickness: 1.5~1.8mm

Analysis of 3. pouring

 

(1) There is no abnormal situation in the pouring of the two gating systems. After the casting is shot, the sand sticking in the runner is not obvious, the surface quality of the casting is good, the structure of the section after the gating system is removed is dense, and the surface does not appear strain and crack.

 

  

Fig. 3 vertical casting-top injectionFig. 4 Sanding-Top Injection

  

Fig. 5 Lining-Top InjectionFig. 5 Lining-Top Injection

 


 

(2) During pouring, the resin sand gate of individual castings was not fixed and lifted up, resulting in sand roll. In order to prevent the gate from lifting up, the gate is placed in the plastic white mold, and the negative pressure system is used to fix it, and good results are achieved.

Fig. 7 Gate Treatment

 

(3) Because the resin sand gate (round) and the runner (square) cannot be completely seamless, there is a risk of the coating at the top of the runner being broken during pouring. In order to overcome this hidden danger, a ceramic ring is added to the top of the straight runner for protection, and the pouring effect is obvious.

  

Fig. 8 Protection with ceramic ring Fig. 9 Protection without ceramic ring

 


  

4. balance test

A total of 3 vertical casting parts were processed and balance tests were carried out respectively. Two of them were punched with one hole each and the other was not punched. The test effect was very good. It shows that the castings poured out by vertical casting-top injection can meet the balance performance test. Due to multiple reasons, the balance value data could not be counted and a quantitative analysis could not be made.

  

Fig. 10 Balance Test Fig. 11Balance test

 


 

5. Conclusion

(1) Diesel engine flywheel is a thick and large shape regular casting, and the molten iron temperature should not be too high during pouring to prevent shrinkage.

(2) When designing the gating system, the principle of "cross-pouring cover" can be skillfully used to achieve the purpose of feeding, and the top injection method does not need to set the riser for feeding.

(3) when the pouring system bonding, ensure that the bonding parts are bonded with hot glue to prevent the coating from entering and causing slag inclusion.

(4) Flywheel parts made of HT250 are castings with large wall thickness. The density of white mold is controlled within 20g/L, the thickness of coating should not be too thick, and the negative pressure can be appropriately increased to -0.06mp.

(5) Lost foam casting seems simple, but in fact it is closely linked. The process must be done well in every link before qualified castings can be poured.

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